Abstract: :Cut a regular hexahedron into innumerable parallel fracture planes, in each of which there is a light cone. With observing in the innumerable light cones the variations of the fracture plane sections with the projective sections, and the sections with their own projections,we came to the following conclusions :1) Xray image deformation is due to the function of light cones;2) no matter whether the object projective plane make an angle,the function of the direct incidence and oblique incidence of the lightcone axial beam keeps constant;3) the elliptical eccentricity of each fracture plane section reflects the space deflection of the object, which is the real deformation factor;4) if the elliptical eccentricity of the projective section is respectively bigger than, equal to or less than the elliptical eccentricity of the fracture plane section,the projection length of fracture surface’s centre vertical diameter and the real length is respectively bigger than,equal to or less than the projection length of the horizontal diameter across the centre of that projection and the real length;5) if the object is at an angle to the projective plane,it will lead to the unequal amplification of the fracture surface’s projection;6) the deformation degree is in direct proportion to the thickness of the object, and it is in inverse change to the distance from the point source to the object, but bears no relation to the distance from the object to projective plane;7) the dissertation in the textbooks stands in error.